/Engine/Source/Runtime/Engine/Classes/Kismet/KismetArrayLibrary.h
Add item to array (unique)
The index of the newly added item, or INDEX_NONE if the item is already present in the array
static int32 Array_AddUnique ( const [TArray](API\Runtime\Core\Containers\TArray)< int32 > & TargetArray, const int32 & NewItem )